Exadata Hybrid Columnar Compression (EHCC) FAQ
(Doc ID 1910687.1)
Last updated on JUNE 07, 2024
Applies to:
Exadata Database Machine V2 - Version All Versions to All Versions [Release All Releases]Information in this document applies to any platform.
Purpose
This document addresses the frequently asked questions related to Exadata Hybrid Columnar Compression.
Questions and Answers
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In this Document
Purpose |
Questions and Answers |
What is Exadata Hybrid Columnar Compression (EHCC) |
What are the types of compression available with EHCC ? |
Can CTAS be used to create EHCC tables ? |
How to convert existing / non-EHCC table to use EHCC ? |
How to disable EHCC compression on a table ? |
Can we use DBMS_REDEFINITION online redefinition package for EHCC tables ? |
How does update works for EHCC table ? |
What is Compression Unit? |
How to check compression format for a particular row ? |
How to get estimate of compression ratios for EHCC compression types ? |
How to enable tracing for EHCC ? |
How to query stats about CUs ? |
What storage types are supported for EHCC or HCC ? |
Can we specify different compression type for each partition in a table ? |
Does EHCC support function based indexes ? |
Is EHCC suitable for single row access methods ? |
Does EHCC uncompress CUs to access the data? Will this result in multiple I/Os for a single row access ? |
Can we use EHCC on normal server with SUN ZFS filesystem ? |
What are supported RDBMS version for EHCC ? |
If table is already OLTP compression on, will I be able to enable EHCC on the same table ? |
Does EHCC supports BLOB data type ? |
Does EHCC supports LONG data type ? |
Can both EHCC and OLTP compression will be on for a single table ? |
In a warehouse with rows being added to an EHCC table via ETL, can the new rows be converted to EHCC, or the whole table to be periodically recompressed ? |
Are there any application code changes if we convert tables to EHCC ? |
Can we join a regular table with EHCC table in a query ? |
Which view to check the compression type ? |
What's the difference between query low and query high ? |
Does Oracle Golden Gate supports EHCC from source to target replication ? |
If one table is marked as query high, can it be moved to archive high or any other EHCC method directly ? |
What is the impact on performance if taking a table out of EHCC? specially if the table is large ? |
In EHCC we may have a table to have mix of HCC and OLTP compression. Does this create extra overhead with fetching data when range scan is used ? |
Is the row migrated out of CU when update occurs causing row migration ? |
Default segment size is 8MB, can EHCC compression make it less than 8MB ? |
References |